1. Field of the Invention
The present invention relates to an ink jet recording apparatus and, more particularly, to an ink jet recording apparatus for use in, for example, a facsimile apparatus and having means for detecting any extraordinary ink discharge.
2. Description of Related Art
A conventional recording apparatus used on a facsimile apparatus will be described with specific reference to FIG. 7. A plurality of recording paper sheets P are stacked and held on a cassette 151. The sheets are fed one-by-one by a sheet feed roller 152 to a delivery roller 153 so as to be further delivered to a recording portion B. The recording portion B is of an ink jet recording type and is equipped with a recording head having an array of a multiplicity of nozzles, e.g., 128 nozzles, for performing scanning in a main-scan direction. In operation, ink is jetted from these nozzles so as to record an image on the upper face of the recording paper sheet P as viewed in FIG. 7. After the recording, the recording paper sheet P is conveyed to an eject section along a lower guide 155 by means of a pair of sheet discharge rollers 154 arranged downstream of the recording portion B and is further ejected by means of a sheet eject roller 156 cooperating with an idle roller 157 so as to be ejected to an ejected sheet stacker 158. Successive recording paper sheets thus ejected are stacked on the ejected sheet stacker 158.
The recording head is a cartridge-type head unit which incorporates an ink tank, so that the whole recording head is replaced with a new head when the ink in the ink tank has been consumed. In order to enable color recording while realizing a more compact construction of the whole recording apparatus, the apparatus is designed to mount either of a cartridge for recording in black color and a cartridge for color recording. The carriage for recording in black (referred to as "black recording cartridge", hereinafter) has 128 nozzles which discharge only black ink. In contrast, the carriage for color recording (referred to as "color recording cartridge", hereinafter) has 64 nozzles for black ink and 24 nozzles for each of three primary colors of yellow, cyan and magenta, as well as ink tanks for inks of these four colors. The configuration and the dimensions of the color recording cartridge are the same as those of the black recording cartridge. Thus, the amount of the ink of each color held in the color recording head is not greater than 1/4 that of the black ink held in the black recording cartridge.
Recording apparatuses have been proposed which perform recording on a variety of types of recording mediums such as paper sheets, OHP transparency sheets, and so forth. Among these recording apparatuses, particularly regarded as being useful and promising is the ink jet recording apparatus which performs recording with reduced running cost and at low level of noise by directly jetting ink onto a recording medium.
Use of an ink jet recording apparatus as the recorder in a facsimile apparatus essentially requires detection of any factor or condition of printing failure such as shortage of ink and inferior discharge of ink, in order that the information received by the facsimile apparatus is recorded without fail. Such detection can be realized by a system having a transmissive-type photo-sensor incorporating a light-emitting element and a light-receiving element. In operation of this detection system, a predetermined number of ink droplets are ejected past the space between the light-emitting element and the light-receiving element so that droplets interrupt the light to be received by the light-receiving element so as to cause a change in the level of the sensor output. Any extraordinary state of ink discharge due to reduction in the amount of ink remaining in the ink supply system or a trouble in the head can be detected by checking the sensor output.
The transmissive-type photo-sensor has a lens which is formed integrally with the light-emitting surface of the light-emitting element so that a substantially collimated light beam is projected towards the light-receiving element. Meanwhile, a molded member is provided on the light-receiving surface of the light-receiving element and a fine aperture of a size on the order of 0.7 mm tall and 0.7 mm wide is formed in the molded member in alignment with the optical axis, so that a linear detectable range of about 0.7 mm tall and 0.7 mm wide is defined over the entire region between the light-emitting element and the light-receiving element. The optical axis along which the light-emitting and light receiving elements are optically coupled together extends in parallel with the nozzle array on the recording head, and the distance between the light-emitting and light-receiving elements is greater than the span of the nozzle array. Therefore, when the photo-sensor is mounted such that the optical axis coincides with the line along which the nozzle array extends, ink droplets discharged by any nozzle of the nozzle array fly across the above-mentioned detectable region between the light-emitting and light-receiving elements. The droplets which intersects the detectable region interrupt the light from the light-emitting element so that the quantity of light reaching the light-receiving element is reduced, thus causing a change in the level of the output derived from the light-receiving element. When the amount of change in the output level observed exceeds a predetermined level, the discharging condition is judged as being normal, otherwise the discharging condition is judged as being extraordinary and defective. When such an extraordinary state is found, the apparatus suspends further recording operation and takes necessary measures such as prohibition of receipt of facsimile message or storage of received facsimile data in a memory, until a suitable recovery operation is performed by, for example, applying suction vacuum to the nozzles to recover the normal ink jetting condition.
The above-described detection system is considered practical and effective because it enables detection of any extraordinary state of ink discharge without requiring any expensive components to be added to the recording head.
Basically, the above-described operation for detecting any ink discharge failure is conducted on all the nozzles of the recording head, upon completion of recording on each of successive recording sheets.
The technique described above, however, has the following problem. It is to be noted that the position of the optical axis of the transmissive-type photo-sensor tends to fluctuate with respect to the path of the discharged ink droplets in the main-scan direction, due to mechanical or dimensional error incurred in the course of fabrication of the apparatus. It is therefore necessary to consecutively discharge the ink over a range wide enough to cover the above-described detectable region, so as to accommodate the fluctuation of the position of the optical axis with respect to the path of the ink droplets. Consequently, the amount of the ink to be spent for the detection of any ink discharge failure is as large as 2% of the total ink consumption, assuming that 75 droplets are discharged from 128 nozzles and that a standard text to be printed has a black-to-white ratio of 4%. This obviously leads to an increase in the running cost. A demand therefore exists for reducing the amount of the ink to be consumed for the purpose of detection of the ink discharge failure from the nozzles of the recording head.
As stated before, a color printer is available which can selectively mount either a black recording cartridge and a color recording cartridge. When this type of color printer is used as the printing means of a facsimile apparatus, it is quite possible that the facsimile apparatus receives data while the printer still carries the color recording cartridge. Detection of ink discharge failure has to be conducted even when the cartridge present on the facsimile apparatus is the color recording cartridge. Despite the fact that the received data can be printed with the black ink alone, all the nozzles on the recording head, including nozzles for different color inks, have to be checked for any discharge failure in the same sequence as that performed on the black recording cartridge. This leads to a serious rise of the running cost. Moreover, since the capacity of the ink tank for each color is small in the color recording cartridge, frequent exchange of the cartridge is required because the ink is consumed away shortly due to repeated discharge failure detecting operation. In addition, a large volume of ink absorber such as of felt has to be installed in order to absorb and retain the ink which has been discharged for the purpose of the detection of ink discharge failure, making it difficult to cope with the demand for the reduction in the cost and the size of the apparatus.